I once hold a coin and suddenly the coin that is almost $1 dump to less than $0.01 to me I move on but to some people which are newbies this can discourage them from participating in crytocurrency and make them conclude it is fraud and that brought me to a question how do you think pump and dump group are damaging crypto-currency and it's reputation??
Well, the thing with pump and dump groups nowadays is that the admins are the ones earning money. Everyone else are literally just pumping the money in for the admins, because the admins are the ones who buy in the coins for cheap before signals are released.
That itself can mislead a lot of people into thinking that pump and dump groups are a good way of making money, especially newbies. That will definitely impact newbies perception of BTC.
Also, as you mentioned, if you as an outsider see a coin being dumped to the ground all of a sudden and result in massive losses, you tend to be a lot cautious in your approach. Which is actually a good thing in some regards, but still damages the overall reputation of crypto to outsiders. But the overall impact is the biggest on the participants in the pump and dump groups, who will lose money in the long run.